The purpose of the proposed study is to prospectively examine exercise self-efficacy and exercise adherence in adults with chronic obstructive pulmonary disease (COPD) by testing a measurement model of exercise self-efficacy. There is compelling evidence that exercise is an effective intervention to increase exercise performance, decrease breathlessness, and improve quality of life of adults with COPD (ACCP/AACVPR, 1997). To sustain these benefits of exercise, adherence to regular exercise is necessary because deconditioning occurs rapidly after cessation or significant reduction of exercise. In fact, many benefits of exercise are often lost within 6 to 12 months after completing exercise interventions that required 1 to 3 months to deliver. Disappointingly, less than 50% of adults will adhere to a regular exercise program. Reasons for the lack of adherence are unclear and require further investigation. In summary, exercise is effective; however, exercise adherence remains a significant problem. The long-term goal of this project is to increase physical activity and improve the quality of life of adults with COPD by improving exercise adherence. Founded on theoretical and empirical support, the Principal Investigator has developed an exercise adherence conceptual model to guide a program of research in exercise adherence in people with COPD. This conceptual model includes exercise self-efficacy, exercise motivation, exercise adherence, and outcomes of exercise. Before exploring the relationships in the exercise adherence conceptual model, it is important to specify and validate measurement models for each element of this conceptual model. Therefore, in this proposed study, the Principal Investigator has carefully specified an original measurement model for the domain of exercise self-efficacy, and disease severity) to be tested. Specific aims of this study are: 1. Confirm the reliability and validity of the self-regulatory efficacy measure in subjects with COPD, and 2. Prospectively test the exercise self-efficacy measurement model. Validated instruments are available for each component of the exercise self-efficacy measurement model. All instruments except the self-regulatory efficacy scale also have been validate in a sample of individuals with COPD. To achieve aim 1, a correlation study design and tests of internal consistency and construct validity will be used. To achieve aim 2, a cross-sectional descriptive design and structural equation modeling will be used. A sample of 236 subjects with mild to severe COPD will be enrolled over 29.5 months. Results of this study will provide new knowledge to guide the development of interventions that can improve exercise adherence and maintain the many benefits of exercise in people with COPD.